A photosensitive composition in a liquid state containing a compound which undergoes a polymerization reaction due to, e.g., irradiation with light or ionizing radiation is used in photosensitive lithographic printing plate materials, resists for printed wiring board fabrication, the production of color filters, and the formation of fluorescent patterns. Photo-curable or ionizing radiation-curable inks for various printing methods and for ink-jet recording may be used in the liquid state as they are. Thus, there are a variety of fields to which the photosensitive composition utilizing photopolymerization can be applied, and, with respect to the use as, for example, a photoresist or a lithographic printing plate, in which an organic solvent or a strongly alkaline reagent is used in the developing treatment, recently, a system which enables a developing treatment using, e.g., water is being developed, and chemicals and apparatuses in association with the developing treatment in such a system are easy to handle and the development of this system is extremely advantageous from the viewpoint of preservation of the environment. Particularly, with respect to the lithographic printing plate, recently, a computer-to-plate (CTP) technique has been developed in which digital data produced on a computer is not output onto a film but directly output onto a printing plate, and the development of various types of plate setters having various lasers as an output device and photosensitive lithographic printing plate materials applicable to them have been vigorously made. As the CTP system is spreading, important problems to be solved and demands for the system include those related to the developing treatment. In a general CTP system, a photosensitive lithographic printing plate material is subjected to exposure with a laser, and then the non-image portion is dissolved using an alkaline developer, and subjected to washing with water and gumming steps, and the resultant material is used in printing. The alkaline developer is harmful to human body, and must be handled and stored under control with satisfactory care. Further, the purchase cost of the alkaline developer and the cost for disposal of the waste developer cause a great burden on a user, and, in addition, solution properties of the alkaline developer, such as pH and temperature, must be controlled with enormous care, making the handling of the alkaline developer extremely cumbersome.
For avoiding the use of the alkaline developer, a photosensitive composition capable of being developed using water has been proposed. For example, Japanese Unexamined Patent Publication No. Hei 5-27437 (patent document 1) discloses an aqueous photosensitive composition comprising a carboxyl group-containing resin, an amine compound, a photo-curable unsaturated compound, a photopolymerization initiator, and water. In this system, the photosensitive composition is used in the form of an aqueous solution or an aqueous dispersion as a coating fluid, and a film of the photosensitive composition is formed on a substrate and used in the state of a dry film, but the photosensitive composition is not suitable for storage for a long term, and a problem is caused in that the developing property of the composition becomes poor with the passage of time, or the photopolymerization initiator used in the composition decomposes with the passage of time, so that the sensitivity of the composition becomes poor or disappears.
Japanese Unexamined Patent Publication No. 2002-174898 (patent document 2) discloses a photosensitive composition having an urethane oligomer having a polyoxyalkylene structure dispersed in water. In this case, a film of the photosensitive composition having excellent flexibility can be obtained, but there is a problem in that with respect to the photosensitive composition which has been stored in an atmosphere at a high humidity, the film of the composition is likely to cause blocking.
Japanese Unexamined Patent Publication No. 2003-215801 (patent document 3) and Japanese Unexamined Patent Publication No. 2008-265297 (patent document 4) disclose a photosensitive composition which is capable of being developed using water and which uses as a binder polymer a cationic or anionic water-soluble polymer having a polymerizable double bond group on the side chain thereof, and a photosensitive lithographic printing plate material using the same. In this system, the problems about the storage stability caused in the above two examples are unlikely to be caused, and there can be provided a photosensitive composition which is unlikely to suffer a change in the sensitivity over a long term and to cause blocking; however, the photosensitive composition has other problems about the developing treatment stability and image quality. Specifically, with respect to the developing treatment stability, various problems arise as follows. As a developing treatment using water is continued, the generation of sludge derived from the constituents of the photosensitive composition in the developer repeatedly used is marked, and especially when using an automatic developing apparatus, a filter provided in a circulating system is clogged with the sludge in a short term during the circulation of the developer, so that the frequency of filter exchange is increased. In addition, the sludge adheres to the surface of a dry film of the photosensitive composition to cause an image defect. Further, with respect to the image quality, a problem occurs as follows. In the photosensitive composition, the compatibility between the binder polymer, which is water-soluble, and the photopolymerization initiator and other photosensitive components, which are hydrophobic, is so poor that phase separation is likely to be caused in the photosensitive composition being applied and dried. Therefore, a non-uniform film of the composition is formed, and thus uniform image quality cannot be obtained. In such a case, neither high image quality nor satisfactorily high sensitivity are achieved, and the improvement of them has been desired.
Further, with respect to the photosensitive composition described in patent documents 3 and 4, the composition in the state of a coating fluid used in the production process has poor storage stability, and the time during which the sensitivity of the composition can be maintained (pot life) is short. Specifically, in the photosensitive composition in the state of a coating fluid, a heat polymerization or photopolymerization reaction is initiated, so that the reaction consumes the photopolymerization initiator and monomers, causing a problem in that, for example, the photosensitive lithographic printing plate material formed after drying the applied composition is reduced in sensitivity.
Furthermore, as photosensitive compositions having a long pot life, Japanese Unexamined Patent Publication No. Hei 5-331240 (patent document 5) discloses a photosensitive composition of a system containing a triazine derivative, and Japanese Unexamined Patent Publication No. Hei 9-68801 (patent document 6) discloses a photosensitive composition of a system using a specific photosensitive resin. However, in these systems, it is difficult to obtain a satisfactorily high sensitivity. Further, it is well known that the addition of an antioxidant, such as a hydroquinone, improves the pot life, but, in this method, the antioxidant induces a polymerization termination reaction, making it difficult to obtain a photosensitive composition having a high sensitivity.